Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to disk drive suspensions, and more particularly to wireless suspensions in which the flexure is wireless and comprises a laminate of plastic film, trace conductors, and a metal layer. In a specific aspect, the invention relates to the manufacture of suspension flexures and, particularly, to the continuous protection of the trace conductors from environmental corrosion, to avoid maleffects including introduction of aerosol particulate contaminants into the assembly process and eventual inadvertent shunting or shorting out of the assembled parts.
2. Description of the Related Art
Environmental exposure of portions of copper conductors has been a problem for many years. Various approaches have been tried. For example, so-called conformal coatings, generally a varnish-like covering material, have been used on suspension arm assemblies such as the IBM 3350/70/80 arm assemblies from the 1970""s and 1980""s. This material resisted solvents and the different atmospheres encountered in the manufacturing and the user environment. Applied by hand, use of the material required a heat cure cycle.
It has been proposed to use a non reactive or non corrodible material for the traces, such as gold. At present, however, the precursor three-layer laminate material used for flexible circuitry and the invention flexures is not available with a gold layer that would enable production of circuitry comprising a gold/polyimide/stainless steel laminate; presently only a copper/polyimide/stainless steel laminate is available.
Better control of the manufacturing environment has been attempted to minimize the noted corrosion problems, e.g., by improving storage and handling procedures to reduce the time the part is exposed to the worst environment. The parts are stored in nitrogen gas-backfilled or vacuum containers pending processing. This approach, however, does not address contamination and corrosion impacts on reliability at the user level where the environment is not so well controlled.
It is an object of the invention, therefore, to provide a better solution to the problem of environmental corrosion of exposed copper conductive traces in wireless flexures and to thereby lessen or eliminate results of such corrosion including contaminating aerosols and shunting of conductors. It is a further object to provide an improved wireless flexure manufacturing process in which the copper pigtails (continued extents of the trace conductors that are not operating parts of the assembly) at the locus of severing are reliably severed to free each flexure from the panel of flexures and, in a preferred embodiment, at the same time encased in insulating plastic film. It is a further object to provide in the course of a laminate flexure manufacturing operation a part that has its copper continually encased with plastic film, and in a preferred embodiment, totally free of exposed copper. It is thus an object to thereby prevent any particles or conductive paste associated with the copper conductors isolated from the environment and blocked from creating harm.
It is a highly specific object to provide a manufacturing process for a wireless flexure and a flexure product in which the conductive traces are modified at their pigtails to be of lesser cross-section, such that a current passing through the traces will preferentially melt the reduced cross-section and sever the trace pigtail there. Heat conducted to the surrounding plastic film at the locus of severing also serves to melt the plastic film layer at the locus and the melted plastic will reduce or eliminate copper exposure and block loss of contaminants from the copper into the surrounding environment.
These and other objects of the invention to become apparent hereinafter, are realized in the invention manufacturing process for flexures for disk drive suspensions that comprise a laminate of a plastic film and conductive traces, which includes defining a plurality of flexures in the laminate each having a predetermined perimeter that is spaced from the predetermined perimeters of adjacent flexures, maintaining a continued extent of the conductive traces across their respective flexure predetermined perimeters to electrically connect the conductive traces to a common conductor, and separating the conductive traces of individual flexures from the laminate by selectively melting the trace continued extents to sever the individual flexure conductive traces from the remainder of the flexures defined in the laminate and melt adjacent plastic film thereonto in exposed conductive trace-free relation.
In particular embodiments, the invention process further includes employing as the laminate a laminate of the plastic film, the conductive traces and a third layer comprising steel, defining a reduced cross section portion in the trace continued extent, and applying a current across the portion to selectively melt the portion while leaving the balance of the trace conductors intact, providing a contact pad on the flexure electrically connected to the trace continued extents, connecting the trace continued extents to a ground, and passing a sufficient current from the pads to ground through the continued extent portions to differentially melt the portions selectively from the remainder of the trace conductors.
In its product aspects, the invention provides a flexure for a disk drive suspension comprising a laminate of plastic film and trace conductors, the flexure having a predetermined perimeter, the trace conductors being generally of a first cross-section, the trace conductors having continued extents extending to and beyond the perimeter of the flexure, the continued extents defining a locus of severing for detaching the flexure from surrounding laminate adjacent the flexure predetermined perimeter, the continued extents having a portion with a reduced cross-section from the first cross-section at the locus for melting preferentially in response to a current passed through the trace conductors and the reduced cross-section portion.
In this and like embodiments, typically, the plastic film comprises polyimide resin, the conductive traces are formed of copper deposited onto the plastic film, the cross-section of the conductive traces is generally about 0.002 by 0.0007 inch, the cross-section of the reduced cross section portion being about 0.0004 by 0.0007 inch, the reduced cross section portion is melt-severed in trace conductor interrupting relation at the locus, the portion within the predetermined perimeter of the flexure preferably being encased in melted plastic film.
In a further embodiment, the flexure laminate further comprises a third layer comprising a spring steel. As in previous embodiments, typically the plastic film comprises polyimide resin, the conductive traces are formed of copper deposited onto the plastic film, the cross-section of the conductive traces is generally about 0.002 by 0.0007 inch, the cross-section of the reduced cross section portion being about 0.0004 by 0.0007 inch, and, the reduced cross section portion is melt-severed in trace conductor interrupting relation at the locus, preferably with the portion within the predetermined perimeter of the flexure being encased in melted plastic film.
In a further embodiment, the invention provides a panel comprising a laminate of plastic film and trace conductors, the panel defining multiple, individually separable flexures for disk drive suspensions, each individual flexure having a predetermined perimeter and trace conductors generally of a first cross-section and having continued extents extending to and beyond the perimeter of the flexure that define a locus of severing for detaching the flexure from surrounding laminate adjacent the flexure predetermined perimeter, the continued extents each having a portion with a reduced cross-section from the given cross-section at the locus for melting preferentially in response to a current passed through the trace conductors and the reduced cross-section portion.
In this and like embodiments, typically, the plastic film comprises polyimide resin, and the conductive traces are copper.